Inner ventilation blade

ABSTRACT

A blade, for example of a high-pressure turbine, is designed with an internal partition ( 9 ) closest to the trailing edge ( 7 ), the upper portion of which ( 20 ) veers towards this edge, in order to improve ventilation of the cooling gases in the area of the apertures ( 15 ) of this edge, and more generally the ventilation of the upper corner of the blade, through the creation of new apertures ( 14′ ) in the apex ( 11 ), or by moving apertures ( 12 ) starting in the second cavity and leading to the intrados in the area of the trailing edge.

The subject of this invention is an inner ventilation blade.

Blades of turbomachines are subject to often very high temperatures, and can be fitted with devices for cooling by gas ventilation, using gas such as the relatively cool gas drawn from the main flow airstream in the area of the compressors; it then flows as far as cavities hollowed out inside the blades, and exits from them through piercings which notably emerge in the intrados and in the trailing edge, where the lower external pressure contributes to the gas flow. These devices are now tried and tested, and generally give satisfactory results, but progress still remains to be made when the ventilation is found to be insufficient due to particularly difficult conditions (for example, in the case of high-pressure turbine blades, which are subject to the highest temperatures), or in certain particular areas of the blades. French patents 2 833 298 and 2 834 015 describe trailing edge ventilations.

Cooling faults, which lead to very high temperatures and certain kinds of damage (burns), have thus been observed at the apexes of certain blades, and more specifically in the corner between the trailing edge and the outer edge. The object of the invention is to resolve this particular problem.

In its most general form the invention concerns a blade including inner cavities where cooling gases can flow, where the cavities are separated by partitions, where one of the partitions, the one closest to a trailing edge of the blade, is more inclined towards the trailing edge from a height of at least 70% of the blade, as measured from a platform to the apex of the blade at an outer edge radius (this measure improves the cooling of the corner of the blade through improved ventilation of the trailing edge, for the reasons which shall be given below), characterised in that one of the cavities delimited towards the trailing edge of the blade by the said partition closest to the trailing edge of the blade includes a series of piercings leading to a lateral face of the blade, where the said piercings emerge in the said cavity through apertures made in a line parallel to the said partition. This improvement thus improves the cooling of the corner of the blade, this time by improved ventilation of the lateral faces (intrados or extrados).

The greater inclination is advantageously gradual, giving the partition a general rounded shape.

The invention will now be described in greater detail by means of illustrative embodiments in connection with the figures:

FIG. 1 and FIG. 2 are general views of the blade in accordance with the invention,

FIG. 3 is a detail showing a prior design which is improved by the invention,

and FIG. 4 is a corresponding detail of a design in accordance with the invention.

FIGS. 1 and 2 show a blade (1), which is attached to a root (2) housed in a disk, which is not represented, and fitted with a platform (3). Blade (1) is hollow and pierced with multiple cavities (4), separated from one another by partitions (5) extending in an essentially radial direction from the root (2) to the apex (11) of the blade (1). In the remainder of the account a distinction shall be made between a cavity (6) closest to the trailing edge (7) of the blade (1), a cavity (8) adjacent to the previous one, and a partition (9) separating them, which is therefore the partition closest to the trailing edge (7).

Ventilation gas arrives in the cavities (4) (and (6) and (8)) through their origins (10) in the root (2) from another region of the machine to which the blade (1) belongs, and rises to the apex (11) of the blade (1); it leaves the cavities gradually through piercings (12) emerging in the intrados (13) and/or in the extrados (22) of the blade (1), whilst other piercings (14) (represented in FIGS. 3 and 4) emerge in the apex (11), and finally by other piercings (15), exiting solely from cavity (6), which emerge in the trailing edge (7).

Ventilation of the apex (11) of the blade (1) is more difficult since the piercings (14) are located at the end of the cavities (4) and since the ventilation gas flow rate is lower and is of lower pressure; another unfavourable circumstance results from the fact that the apex (11) consists of a thin external ridge (16), extending on the extrados side and on the intrados side of the blade, thus forming a hollow cavity referred to as a “basin” (17). Ridge (16) enables the hot gas outflows between the apex of the blade and the casing opposite it to be limited, and is a zone which is subjected to wear and tear zone when the blade, under the combined effect of the thermal expansion and the centrifugal force, extends and touches the casing opposite it. The basin (17) and the ridge (16) are regions which are difficult to cool; the situation is especially critical in the upper corner (18) of the blade (1) adjacent to the trailing edge (7), where the cavity (6) is narrowest.

Reference should be made to FIG. 3. In the habitual design the partition (in this case 9′) closest to the trailing edge (7) is rectilinear, as are the others, to simplify blade manufacture, and it is generally completely radial in direction. The inventors observed the existence of a low-speed recirculation zone (19) in the cavity (6) at the point where the partition (9′) and wall at the base of the basin (17) connect. The low dynamic pressure of the ventilation gas in this location makes the creation of upper piercings to ventilate the apex (11) futile, such that the edge of the basin (17) is not ventilated at all; and it is observed that the piercings (15) leading to the trailing edge (7) closest to the apex (11), typically the three or four closest such piercings, are subjected to a particularly low flow rate due to the low pressure of the gas.

The modification specific to the invention, which can be seen in FIG. 4, consists in giving the partition (9) closest to the trailing edge (7) an upper end (20) which is more inclined towards the trailing edge (7) than the remainder of the partition (9), and which is advantageously increasingly inclined, with a rounded shape, and an almost regular connection, to the wall at the base of the basin (17). The upper portion (20) can start at 80%, or possibly 70%, of the height of the blade (1) measured from the platform (3) as far as the outer edge, i.e. the wall at the base of the basin (17). The other partitions remain rectilinear. The technical effects are as follows: the low-speed recirculation zone (19) disappears; the guiding of the ventilation gas to the piercings (15) close to the apex (11) is improved, and its pressure is increased, which also increases the flow rate through these upper piercings (15); the piercings (12) leading to the intrados (13) (or to the extrados) from the second cavity (8) can be moved towards the trailing edge (7), with their apertures (21) in the second cavity (8) occupying a line parallel to the upper portion (20); at least one additional apex piercing (14′) can be included due to the fact that the second cavity (8) is widened at the apex (where the first cavity (6), in the design represented here and also in the prior design, normally has no piercings (12) and (14) at the apex due to greater ventilation difficulties). The effect of all these modifications is that the upper corner (18) of the blade (1) is better ventilated and cooled, in the trailing edge (7) by the piercings (15), in the lateral intrados (13) or extrados face by the moved piercings (12), and also in the basin (17) by the additional apex piercing or piercings (14′). 

1. A blade (1) including internal cavities (4, 6, 8) for the circulation of cooling gases, where the cavities are separated by partitions (5, 9), where one of the partitions (9), that closest to the trailing edge (7) of the blade, is more inclined towards the trailing edge from a height of at least 70% of the blade, measured from a platform (3) of the blade to an outer edge radius, characterised in that one of the cavities (8), delimited in the area of the trailing edge of the blade by the said partition (9) closest to the trailing edge of the blade, includes a series of piercings leading to a lateral face of the blade, where the said piercings emerge in the said cavity (8) through apertures (21) placed in a line parallel to the said partition (9).
 2. A blade according to claim 1, characterised in that the greater inclination gradually becomes less great. 